The invention relates to implantable medical devices. More particularly, the invention relates to programmable functions in such devices.
Implantable medical devices (IMDs), such as implantable cardioverter/defibrillators (ICDs) and pacemakers (PMs), can detect and administer therapy for a variety of conditions. These conditions include ventricular fibrillation (VF), atrial fibrillation (AF), tachycardia, and bradycardia. As a particular example, an ICD receives electrical signals from the heart and processes these signals to monitor cardiac rhythms. The ICD typically includes leads that extend into the heart and support two or more defibrillation electrodes. When the ICD detects an abnormal cardiac rhythm, such as ventricular fibrillation, the ICD may deliver an electrical shock to the heart via a defibrillation electrode to restore the normal cardiac rhythm.
Under certain circumstances, it may be desirable to disable the operation of one or more functions of an IMD. For example, some operating conditions may make an ICD prone to false detection of ventricular fibrillations or other abnormal rhythms, i.e., detection of a VF when none is actually present. These operating conditions include electrocautery, diathermy, and other surgery-related procedures that involve the application of electromagnetic energy. Such procedures may generate electrical noise that interferes with accurate detection and analysis of cardiac signals.
Electrical interference resulting from such procedures may have many adverse effects. For example, the ICD may prematurely begin a blanking interval and ignore legitimate cardiac signals. As a result, the ICD may detect an arrhythmia that is not actually present and, in response to the perceived arrhythmia, deliver a defibrillation shock. This shock may provide inappropriate therapy to the patient and subject a health care provider to dangerous electric shocks.
Accordingly, surgical procedures that employ the application of electromagnetic energy may warrant temporarily disabling detection of and therapy for VF and other abnormal cardiac rhythms. Other circumstances may also warrant disabling VF detection and therapy, such as ICD oversensing troubleshooting. In addition, a do-not-resuscitate order issued by a physician may warrant permanently disabling VF detection and therapy, as well as other functions of the ICD.
One way to disable defibrillation is to temporarily deactivate the arrhythmia detection function of the ICD. Some ICDs include a reed switch, Hall switch, or other magnetically operated switch coupled to the circuitry that controls defibrillation. Placing a magnet in transcutaneous proximity to the ICD activates the switch and temporarily deactivates the arrhythmia detection function of the ICD, thereby preventing the application of defibrillation pulses.
When the magnet is moved away from the ICD, the arrhythmia detection function is re-enabled. Although using a magnet to suspend a function of an implantable device is relatively simple, this approach can fail if the magnet is improperly placed or if the magnet shifts from its proper location. In addition, it is difficult to use a magnet to disable detection and therapy functions permanently in appropriate situations, such as compliance with a do-not-resuscitate order.
Defibrillation can also be disabled by a programmer external to the ICD. To disable defibrillation, the programmer transmits a control signal to the ICD, which responds by disabling detection, therapy, or both. As a result, the ICD may stop detecting VF or other arrhythmias, or may continue detecting VF but stop administering electric shocks. In any case, once disabled, defibrillation remains inactive until reactivated by another control signal.
One problem that has been observed in connection with the use of a programmer is that health care providers sometimes inadvertently fail to reactivate defibrillation. Leaving VF detection or therapy in the disabled state places the patient at risk because no life saving therapy is administered during subsequent VF episodes. In some cases, ICDs could be inadvertently left in the disabled state for days or even months, with potentially fatal consequences.
The invention is generally directed to techniques for issuing a notification when an ICD or other medical device has been left in a programmed state for some time, possibly inadvertently. For example, the medical device may issue the notification if ventricular fibrillation (VF) detection or therapy has been left in a programmed disabled state for an extended period of time. In some embodiments, the notification is issued to the patient, who may then take corrective action, such as visiting a health care provider. Alternatively, the health care provider may receive the notification and contact the patient.
One particular embodiment of the invention is directed to a method for indicating a programmed state of an implantable medical device. The programmed state is detected. At a subsequent time after detecting the programmed state, it is determined whether the implantable medical device is in the same programmed state. If so, a notification is issued. This method may be implemented using a processor-readable medium, such as a read-only memory (ROM).
The invention may also be embodied in an implantable medical device that includes a control module programmable to a programmed state. A monitoring module is capable of detecting the programmed state. An alert module issues a notification when the control module remains in the programmed state at a subsequent time after the monitoring module detects the programmed state.
The invention is capable of providing one or more advantages. By alerting a patient when the implantable medical device has been left in a potentially harmful programmed state for an extended duration, the invention may mitigate the risk of harm to the patient due to human error. For example, if ventricular fibrillation (VF) detection or therapy is programmed to a disabled state and inadvertently left in that state, i.e., is not enabled again in a timely manner, issuing an alert to the patient may prompt the patient to make an office visit to have VF detection and therapy reactivated. In addition, in some embodiments, life-critical features, such as VF detection and therapy, may be automatically reactivated without human intervention.
The above summary of the invention is not intended to describe every embodiment of the invention. The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.